Field emission is usually realized from sharp tips having radii of curvature in the range of micrometers and nanometers. There are several methods for their preparation.
One of them consists in growing of oriented, mutually parallel whiskers on a substrate and, then, sharp tips are prepared from the whiskers by various treatments.
To this aim, chemical vapor deposition of crystals, including chemical transport of substances, is most suitable. It is known a method for crystallization of materials in a narrow space [1]. However, this method is not effective for growing of oriented whisker arrays, because it does not ensure nucleation and growth of whiskers at particular points of substrates.
It is known a method for growing of oriented whisker arrays on a single-crystalline substrate oriented along the most-close-packed crystallographic face of a given material by vapor phase deposition, at heating, via solvent (liquid-forming) particles orderly deposited on the substrate [2]. This method is based on the vapor-liquid-solid (VLS) growth mechanism proposed by the same author [3]. However, the method and apparatus patented and described for its realization suffer from the fact that the grown whiskers are often branching, kinking, etc.
In the scopes of the mentioned method for whisker growing, a procedure for creation of localized (e.g., micron-sized) solvent particles is important. For growing of, e.g., silicon whiskers, metals, such as gold, copper, nickel, etc, are used as solvents.
One of the technique for preparation of the localized particles consists in evaporation of the metals through a template mask. However, such a technique is unsuitable for localization of the particles on large-area substrates (for example, cm.sup.2 or more), because, in such a case, it is impossible to ensure a uniform clasp of the template to the substrate. On this reason, the metal particles formed are not clear-cut, have different sizes, etc.
More suitable for this is a photolithographic process. Such a process, as applied to whisker growth, is described in [4]. This method, however, gives a poorly-reproducible results because the solvent used (e.g., gold) contacts with the photoresist at a preliminary stage of the procedure resulting in a non-controlled, non-oriented growth of whiskers.
Another photolithographic method for localization of the solvent is described in [5]. There, the solvent (gold) is deposited inside an oxide mask formed on silicon substrate. However, the method suffers from the fact that the liquid alloy (silicon-gold in this case) is spreading, at high temperature, along the substrate-oxide interface, "exploses" the oxide and, accordingly, an ordered whisker growth is destroyed.
It is known an apparatus for growing of oriented whisker arrays that consists of a tube reactor with a gas-mixture that flows through the reactor evolving the crystallized material, of an axis-symmetric substrate holder and a heating source [6]. The apparatus, however, has a figured shape heater with cavities for placing of the substrates. Such a heater does not allow to reach an ordered, uniform, perfect growth of whiskers on large areas due to fluctuations of the gas streams, a non-uniform temperature gradients, etc.
Tasks of this invention are the following:
(1) A method for controlled growing of whiskers on a substrate that allows to prepare regular arrays of well-oriented whisker arrays on a large area. This method must also include techniques for deposition of arrays of localized solvent particles on the substrate. PA1 (2) Apparatus for realization of the method for controlled growing of the whisker arrays on a substrate that pprovides preparation of such arrays uniform on large areas.